1. Field of the Invention
The present invention pertains to damping servo motor control mechanisms and more particularly pertains to a belt drive system (e.g. in photocopiers) having a main servomotor for driving a drive roller which drives a belt and a damping servomotor which dampens the velocity of an idler roller attached to the belt so that the velocity of the belt at a location near the idler roller is maintained constant. 2. Discussion of the Related Art
The prior art is replete with examples of drive-belt mechanisms.
U.S. Pat. No. 4,799,981 to Stone et al. discloses a servo control mechanism to accurately wind and unwind a tape web from two spools to accurately apply strips or courses of tape carried by the web to a contoured surface. U.S. Pat. No. 4,457,506 to Ashbee discloses a servo-controlled recirculating automatic document feeder which transports a document along a simplex or duplex path. U.S. Pat. No. 4,318,540 discloses a constant spacing document feeder which provides constant spacing between documents of various length by means of a variable speed DC motor which drives a feed wheel.
U.S. Pat. No. 3,988,017 to Kyhl discloses a belt-driven work piece feeding device which uses a plurality of friction feeders to address the problem of feeding letters of various sizes through the device. U.S. Pat. No. 4,819,927 to Noguchi et al. discloses a flat article feeding apparatus which comprises a plurality of reversibly driven and individually urged pulleys. A first driving means drives an endless feed belt and an urging means urges the idler pulleys towards a feed plane so as to come in contact with a flat article. A second driving means drives the idler pulleys to make the pulleys reversedly feed the article. The pulleys are controllably driven in response to a completion signal.
In printers and photocopy devices, it is essential that printing belts be driven at a constant velocity. If printing occurs during a time when light intensity is constant and the velocity of the printing belt varies, light and dark bands will appear on the printed page (i.e. banding).
In color and high quality xerography the problems of banding are especially important to address. Tests have shown that any banding that shows up at a cycle per millimeter will be easily detected by the human eye (the eye being less sensitive to larger wave lengths and to shorter wave lengths).
Accordingly, a need is seen for a mechanism to control belt speed so as to achieve uniform printing quality.